Package structures and methods for forming the same

ABSTRACT

A device includes a redistribution line, and a polymer region molded over the redistribution line. The polymer region includes a first flat top surface. A conductive region is disposed in the polymer region and electrically coupled to the redistribution line. The conductive region includes a second flat top surface not higher than the first flat top surface.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional of U.S. patent application Ser. No.13/298,102, entitled “Package Structures and Methods for Forming theSame,” filed on Nov. 16, 2011, which application is incorporated hereinby reference.

BACKGROUND

The fabrication of modern integrated circuits typically involves severalsteps. Integrated circuits are first fabricated on a semiconductorwafer, which contains multiple duplicated semiconductor chips, eachcomprising integrated circuits therein. The semiconductor chips are thensawed from the wafer and packaged. The packaging processes have two mainpurposes: to protect delicate semiconductor chips, and to connectinterior integrated circuits to exterior pins.

In conventional packaging processes, a semiconductor chip may be mountedon a package component using flip-chip bonding. An Underfill isdispensed into the gap between the semiconductor chip and the packagecomponent to prevent cracks from being formed in solder bumps or solderballs, wherein cracks are typically caused by thermal stresses. Thepackage component may be an interposer that includes metal connectionsfor routing electrical signals between opposite sides. The chip may bebonded to the interposer through direct metal bonding, solder bonding,or the like.

With the increasing demand for more functions, package-on-package (PoP)technology is used to further expand the integration ability of thepackages. When the PoP technology is used, packages are stacked. Thereare various designs regarding how the PoP structures can be formed. Byusing the PoP technology, the package design becomes more flexible andless complex. Time-to-market is also reduced for product upgrades. Witha high degree of integration, the electrical performance of theresulting package is also improved due to the shortened connecting pathsbetween the package components.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIGS. 1 through 10 are cross-sectional views of intermediate stages inthe formation of a package in accordance with various embodiments.

DETAILED DESCRIPTION

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

A package structure and the method of forming the same are provided inaccordance with various embodiments. The intermediate stages of formingthe package structure are illustrated. The variations of the embodimentsare discussed. Throughout the various views and illustrativeembodiments, like reference numbers are used to designate like elements.

FIGS. 1 through 10 illustrate the cross-sectional views of intermediatestages in the manufacturing of a package in accordance with embodiments.FIG. 1 illustrates carrier 20 and release layer 22 formed on carrier 20.Carrier 20 may be a glass carrier, a ceramic carrier, or the like.Release layer 22 may be formed of a polymer-based material, which iscapable of being removed later, so that the structures formed overrelease layer 22 may be demounted from carrier 20. Release layer 22 maybe formed of a thermal-release, chemical-release, UV-release, orlaser-release material. In some embodiments, release layer 22 isdispensed as a liquid, and is then cured. The top surface of releaselayer 22 is leveled to have a high degree of co-planarity. Inalternative embodiments, release layer 22 is a laminate film, and islaminated onto carrier 20.

Referring to FIG. 2, redistribution layers 24 are formed on releaselayer 22. Redistribution layers 24 include metal lines 26 and vias 28interconnecting metal lines 26, wherein metal lines 26 and vias 28 areformed in inter-layer dielectrics (ILDs) 30. Metal lines 26 and vias 28are referred to as redistribution lines (RDLs) 26/28 hereinafter. Thebottom layer of redistribution layers 24 may be in contact with the topsurface of release layer 22. In an embodiment, RDLs 26/28 may be formedof metals or metal alloys, such as copper, aluminum, aluminum copper,nickel, or the like. ILDs 30 may be formed of a photo-sensitive materialsuch as polyimide or polybenzoxazole (PBO). Alternatively, ILDs 30 areformed of a nitride such as silicon nitride. In yet other embodiments,ILDs 30 may be formed of an oxide such as silicon oxide, phosphosilicateglass (PSG), borosilicate glass (BSG), boron-doped phosphosilicate glass(BPSG), or the like. In accordance with some exemplary embodiments, theformation of RDLs 26/28 and ILDs 30 may include forming and patterningone of ILDs 30, depositing a metal layer, and then patterning the metallayer. Alternatively, a damascene process may be used, which includesforming ILD 30 as a blank layer, forming openings in the respective ILDs30, filling a metallic material in the respective ILDs 30, andperforming a chemical mechanical polish (CMP).

In an embodiment, metal finish 32 may be formed optionally as a portionof the top layer of RDLs 26/28. In some embodiments, metal finish 32 maybe a nickel layer. In other embodiments, metal finish 32 may be formedof materials and methods, including, but not limited to, electro-lessnickel immersion gold (ENIG), electro-less nickel electro-less gold(ENEG), electro-less nickel electro-less palladium immersion gold(ENEPIG), direct immersion gold (DIG), immersion tin, or the like.

In alternative embodiments, instead of forming redistribution layers 24starting from release layer 22, redistribution layers 24 may bepre-formed and attached onto release layer 22. In some embodiments, apackage substrate may be used as redistribution layers 24.

Referring to FIG. 3, package component 36 is bonded to metal layers 24.In some embodiments, package component 36 is a device die includingactive devices such as transistors (not shown) therein. In Alternativeembodiments, package component 36 is a package that comprises a devicedie bonded to an interposer, a package substrate, or the like. Thebonding of package component 36 to metal layers 24 may be performedthrough connectors 38, which may include solder regions, metal pillar,metal pads, and/or the like. The bonding may be solder bonding, metalpillar to metal pillar bonding, Bum-on-Trace (BOT) bonding, or the like.

FIG. 4 illustrates the formation of Z-interconnectors 40, which arenamed due to their function of connecting features in the direction(Z-direction), which is perpendicular to the major top surface ofredistribution layers 24. Z-interconnectors 40 are alternativelyreferred to as connectors 40 throughout the description. In theresulting structure, at least top portions, and possibly entireties, ofZ-interconnectors 40 comprise solder regions that have round topsurfaces. In some embodiments, Z-interconnectors 40 are solder balls,and are placed on metal finish 32/RDLs 26/28, and then reflowed.Accordingly, the formation of the respective Z-interconnectors 40 mayinclude placing and reflowing Z-interconnectors 40. In alternativeembodiments, Z-interconnectors 40 may have other structures comprising,for example, metal pillars and solder caps on the metal pillars.Accordingly, the formation of the respective Z-interconnectors 40 mayinclude forming a mask layer (not shown), forming openings in the masklayer, plating the metal pillars and the solder caps, and removing themask layer. The solder caps may then be reflowed. As shown in FIG. 4,one of top RDLs 26 includes a first end portion overlapped by, andbonded to, package component 36, a second end having a recess, withZ-interconnector 40 in the recess, and an intermediate portionconnecting the first end portion to the second end portion. Metal finish32 continuous extends through the first end portion, the second endportion, and the intermediate portion.

FIG. 5 illustrates the molding of polymer region 42, which may comprisea molding compound, a molding underfill, an epoxy, or the like. Polymerregion 42 covers package component 36 and Z-interconnectors 40, with topsurface 42A of polymer region 42 higher than top surface 36A of packagecomponent 36 and top surface 40A of Z-interconnectors 40, so thatpackage component 36 and Z-interconnectors 40 are embedded in polymerregion 42.

Referring to FIG. 6, a planarization, such as a grinding process, isperformed to remove a top layer of polymer region 42. A top portion ofeach of Z-interconnectors 40 is also removed during the planarization.As a result, top surfaces 40A of Z-interconnectors 40 are flat, and arelevel with top surface 42A of polymer region 42. The sidewalls ofZ-interconnectors 40, on the other hand, are in contact with polymerregion 42, and are rounded. After the planarization, top surface 36A ofpackage component 36 may be level with, or lower than, top surfaces 40Aand 42A.

FIG. 7 illustrates the optional recessing of Z-interconnectors 40,wherein after the step as shown in FIG. 6 is formed, an etching step isperformed using an etchant that attacks Z-interconnectors 40, and doesnot attack polymer region 42. Accordingly, recesses 41 are formed, andtop surfaces 40A of Z-interconnectors 40 are lower than top surface 42Aof polymer region 42. Top surfaces 40A remain to be substantially flatafter the recessing of Z-interconnectors 40. In an exemplary embodiment,recessing depth D1, which is the height difference between top surfaces40A and 42A, is greater than about 10 μm, for example, althoughdifferent values may also be used.

FIG. 8 illustrates the releasing of carrier 20 from redistributionlayers 24 and the formation of connectors 48. In an embodiment, thereleasing may be achieved by performing a step (such as a UV lightexposure) to cause release layer 22 to lose adhesion, so that carrier 20may be removed from release layer 22. Release layer 22 may then beremoved, resulting in the structure shown in FIG. 8.

FIG. 8 also illustrates the formation of connectors 48 on the bottomlayer of redistribution layers 24, wherein connectors 48 andZ-interconnectors 40 are on opposite sides of redistribution layers 24.In some embodiments, connectors 48 are solder balls, and are placed onthe bottom layer of redistribution layers 24 and reflowed. A singulationmay then be performed along scribe lines 52, so that a plurality ofpackages is formed, wherein each of the packages may be identical to theillustrated package 50.

Next, as shown in FIGS. 9 and 10, package component 54 is bonded topackage 50. As shown in FIG. 9, package component 54 is first placed onpackage 50, with connectors 56 of package component 54 residing onZ-interconnectors 40. In some embodiments, package component 54 is apackage that includes device die 55 bonded to interposer (or packagesubstrate) 57, and hence the resulting structure in FIG. 10 is aPackage-on-Package (PoP) structure. In alternative embodiments, packagecomponent 54 may be another type of components such as a device die.Connectors 56 that are used for bonding may be solder balls, which haveround surfaces, although connectors 56 may have other structures such asmetal pillars and solder caps (balls) on the metal pillars. It isobserved that since the top surfaces of Z-interconnectors 40 are flat,connectors 56 are unlikely to shift on Z-interconnectors 40.Furthermore, in the embodiments wherein the top surfaces ofZ-interconnectors 40 are recessed from top surface 42A of polymer region42, connectors 56 are better confined in recesses 41.

After the surface of connectors 56 are in contact with top surfaces 40Aof Z-interconnectors 40, a reflow is performed to form connectors 58,which join package component 54 to package 50. The resulting structureis shown in FIG. 10.

It is observed that in the resulting structure in FIG. 10, recesses 41as in FIG. 7 may further confine the molten solder during the reflow, sothat the assembly yield for the packaging process is increased.

In accordance with embodiments, a device includes a redistribution line,and a polymer region molded over the redistribution line. The polymerregion includes a first flat top surface. A solder region is disposed inthe polymer region and electrically coupled to the redistribution line.The solder region includes a second flat top surface not higher than thefirst flat top surface.

In accordance with other embodiments, a device includes a redistributionline, and a molding compound molded over the redistribution line,wherein the molding compound comprises a first flat top surface. Asolder ball is disposed in the molding compound, wherein the solder ballis over and bonded to the redistribution line. The solder ball includesround sidewalls and a second flat top surface not higher than the firstflat top surface. A die is disposed over and bonded to theredistribution line, and is located in the molding compound. A topsurface of the die is not higher than the first flat top surface.

In accordance with yet other embodiments, a method includes forming aconnector over and electrically coupled to a redistribution line,wherein the connector include a solder region having a round topsurface. A polymer region is molded to cover the connector and theredistribution line. The polymer region and the solder region are thengrinded, until the solder region forms a first top surface level with asecond top surface of the polymer region.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A method comprising: forming a redistribution structure over a carrier, wherein the redistribution structure comprises dielectric layers and redistribution lines extending into the dielectric layers, wherein a redistribution line in the redistribution structure forms a first recess and a second recess, and the redistribution line comprises a first portion underlying the first recess, and second portions forming sidewalls of the first recess; bonding a device die to the redistribution lines; attaching a conductive region onto the redistribution lines, wherein the conductive region extends into the first recess and is in contact with a top surface of the first portion and sidewall surfaces of the second portions of the first recess; encapsulating the device die and the conductive region in an encapsulating material, wherein the encapsulating material extends into the second recess; performing a planarization step to reveal the conductive region; and de-mounting the device die and the redistribution structure from the carrier after the planarization step.
 2. The method of claim 1 further comprising, after the planarization step, further recessing the planarized conductive region to form a recess, wherein the recess extends into the encapsulating material.
 3. The method of claim 2, wherein the recessing the planarized conductive region comprises etching the planarized conductive region.
 4. The method of claim 2 further comprising: placing a package component, wherein an additional conductive region of the package component has a bottom portion placed into the recess; and performing a reflow to join the conductive region to the additional conductive region.
 5. The method of claim 1, wherein the encapsulating material encapsulates an entirety of the device die, and the planarization step also reveals the device die.
 6. The method of claim 1 further comprising forming a release layer on the carrier, wherein the redistribution structure is formed over the release layer, and in the de-mounting, the release layer is removed from the redistribution structure.
 7. The method of claim 2, wherein the encapsulating material comprises an edge portion overlapping an edge portion of the conductive region, and the edge portion has a top surface, and after the recessing the planarized conductive region, a top surface of the conductive region is lower than the top surface of the edge portion of the encapsulating material.
 8. A method comprising: forming a redistribution structure comprising a redistribution line over a release layer, with the release layer being further located on a carrier, wherein the redistribution structure forms a first recess and a second recess, and the redistribution line comprises a first portion underlying each of the first recess and the second recess, and sidewalls of the redistribution line form sidewalls of each of the first recess and the second recess; forming an electrical connector over and electrically coupling to the redistribution line, wherein the electrical connector comprises a conductive region having a round top surface, and the electrical connector extends into the first recess; molding the electrical connector in a molding compound, wherein the molding compound extends into the second recess; grinding the molding compound and the conductive region, until the conductive region has a first top surface level with a second top surface of the molding compound; and etching the grinded conductive region to recess the first top surface of the conductive region to a level lower than the second top surface of the molding compound.
 9. The method of claim 8, wherein the forming the electrical connector comprises: placing a solder ball on the redistribution line; and reflowing the solder ball.
 10. The method of claim 8 further comprising, after the grinding, bonding a package component to the electrical connector.
 11. The method of claim 8 further comprising: after the grinding, demounting the carrier from the redistribution structure.
 12. The method of claim 8 further comprising, before the molding, bonding a die onto an additional redistribution line of the redistribution structure, wherein after the molding, the die is molded in the molding compound.
 13. The method of claim 8, wherein the redistribution line is in a top redistribution layer of a plurality of redistribution layers, and wherein the method further comprises forming an additional electrical connector attached to a bottom layer of the plurality of redistribution layers.
 14. The method of claim 8, wherein the molding compound comprises an edge portion overlapping an edge portion of the conductive region, and the edge portion has a top surface, and after the grinded conductive region is etched, a top surface of the conductive region is lower than the top surface of the edge portion of the molding compound.
 15. A method comprising: forming a redistribution structure comprising a redistribution line over a release layer, with the release layer being further located on a carrier, wherein the redistribution structure forms a first recess and a second recess, and the redistribution line comprises a first portion underlying each of the first recess and the second recess, and the redistribution line forms sidewalls of each of the first recess and the second recess; disposing a first conductive region extending into the first recess; encapsulating a device die and the first conductive region in an encapsulating material to form a first package, wherein the device die and the first conductive region are embedded in the encapsulating material, and the encapsulating material extends into the second recess; performing a planarization to reveal the first conductive region and a top surface of the device die; after the planarization, recessing the first conductive region; and bonding a second package to the first package through the first conductive region.
 16. The method of claim 15, wherein in the bonding the second package to the first package, a second conductive region of the second package is in contact with a top surface of the recessed first conductive region.
 17. The method of claim 16, wherein the recessing the first conductive region comprises etching the first conductive region.
 18. The method of claim 17, wherein when the first conductive region is etched, the encapsulating material is not etched.
 19. The method of claim 15 further comprising: bonding the device die and the first conductive region to the redistribution structure.
 20. The method of claim 15, wherein the redistribution structure is formed over a carrier, and the method further comprises de-mounting the carrier from the redistribution structure after the encapsulating the device die. 